1/(1×2×3)+1/(2×3×4)+……+1/(98×99×100)=1/2*[(1/(1*2)-1/(2*3)+1/(2*3)-1/(3*4)+……+1/(98*99-1/(99*100)]=1/2*[1/2-1/9900]=1/4-1/19800=(4950-1)/19800=4949/19800？过程？